1. Field of the Invention
The present invention relates to a fold-down automotive seat of the type wherein a seat back thereof may be inclined forwardly and further folded down under biasing force of a spring element onto a seat cushion thereof. In particular, the invention is directed to a structure of such fold-down automotive seat for allowing the seat back to be folded downwards under the biasing force of the spring element, while causing the seat back to stop temporarily at a predetermined point prior to the seat back being folded onto the seat cushion.
2. Description of Prior Art
Most of fold-down automotive seats is provided with a reclining device operable for causing a seat back thereof to incline forwardly of the seat and further fold down onto a seat back. Typically, the reclining device is operatively connected between a lower end of one lateral frame member of seat back frame and a base plate fixed to the seat cushion or to a floor of vehicle. The reclining device includes a connecting tube which is firmly connected between two lateral frame members of seat back frame, so that operation of the reclining device is transmitted via the connecting tube to both of the two lateral frame members, thereby causing both two seat back frame's lateral frame members or a seat back to rotate forwardly and backwardly in adjustable manner. For that purpose, the reclining device has a locking mechanism provided with a control lever (the so-called recliner), which is operable by the control lever to either place the seat back in a locked state or release the seat back from the locked state.
In the fold-down seat of this kind, a coil torsion spring or spiral spring is typically used as a means for giving a biasing force to the seat back in the forward direction of seat in order to enable a user to easily and quickly fold the seat back onto the seat cushion. As is known, the spiral spring has a stationary inward end disposed adjacent to a center thereof and a movable outward end disposed circumferentially thereof. As for example disclosed from the Japanese Laid-Open Patent Publication No 2000-102438, a spiral spring is mounted in the above-stated kind of reclining device, such that the stationary inward end thereof is secured to a securing lug formed in a reclining device connected with a base plate fixed on the side of seat cushion frame, whereas the movable outer end thereof is secured to a securing lug formed on an upper arm connected with a lateral frame member of seat back frame. In this prior art, the reclining device has a locking mechanism for locking the upper arm or the seat back at a desired position against the biasing force of the spiral spring. By operating a control lever of that locking mechanism, a user can adjustingly incline the seat back at a desired angle between forward and backward inclination limit points of seat back.
Most of rear seats is also a fold-down seat of this kind having the foregoing reclining device and spiral biasing spring, with a view to allowing a user to fold the seat back thereof forwardly onto the seat cushion thereof, so that a whole back surface of that seat back lies horizontally upon the seat cushion to provide a load-carrying platform in the backward cabin area of automobile.
However, in such rear seat, the spiral spring always gives a great biasing force attempting to cause forward rotation of the seat back, which has raised the problem that, upon unlocking operation of the locking mechanism of reclining device, the seat back will abruptly rotate forwardly under the great biasing force of spiral spring, and therefore it is of a high likelihood that the seat back may strongly hit a user or cause an unexpected serious trouble.
To avoid the dangerous abrupt inclination of seat back, a damper means has been used for making slow or gentle the biased inclination of seat back when the locking mechanism is operated to unlock the seat back. In this regard, the Japanese Laid-Open Patent Publication No. 2007-050765 teaches a stopper pin formed on the side of a seat back and a movable damper element having an arcuate guide slit. According thereto, when a user unlocks the seat back and the seat back is about to be quickly folded forwardly toward a seat cushion under a biasing force of spring, the stopper pin is displaced along the arcuate guide slit of the movable damper element, while being in a frictional contact with both two edges of that particular arcuate guide slit. The movable damper element is also moved together with the seat back being folded down, and therefore a certain resistance is given to the forward and downward movement of seat back being folded down toward the seat cushion, thereby making slow and gentle the forward movement of the seat back. Hence, it is possible to avoid the abovementioned abrupt forward folding of seat back as well as the serious troubles incidental thereto.
But, such provision of movable damper element makes the structure of seat complicated and large in size and therefore becomes unfavorable in view of the recent demand for weight light and small-sized structure of automotive seat. Further, the movable damper element is not designed to stop the forward inclination of seat back to a horizontal folded-down position where it rests on a seat cushion, with the result that, a precious item placed on the seat cushion will be strongly hit by the downwardly moved seat back and sandwiched between that seat back and the seat cushion under the biasing force of spring. This may result in the item being damaged or broken. Still further, since the seat back always receives the forward biasing force of spring, when trying to return the thus-folded seat back to a normal use position, it is necessary or quite troublesome for a user to use his or her force overcoming the biasing force of spring to move the seat back upwardly to the normal use position.